1. Field of the Invention
The present invention relates to a radiographic image capturing apparatus, and especially to a radiographic image capturing apparatus including a plurality of radiation detecting elements two-dimensionally arranged.
2. Description of Related Art
Heretofore, various kinds of radiographic image capturing apparatuses have been developed, such as a so-called direct type radiographic image capturing apparatus which causes detecting elements to generate electric charges depending on a dose of irradiated radiation such as X-ray and converts the electric charges into electrical signals, and a so-called indirect type radiographic image capturing apparatus which causes a scintillator or the like to convert irradiated radiation into other wavelength light such as visible light and then causes photoelectric conversion elements such as photodiodes to generate electric charges depending on energy of converted and irradiated light and converts the electric charges into electrical signals (i.e. image data). With regard to the present invention, the detecting elements of the direct type radiographic image capturing apparatus and the photoelectric conversion elements of the indirect type radiographic image capturing apparatus are correctively referred to as radiation detecting elements.
The radiographic image capturing apparatus of this type has been known as a Flat Panel Detector (FPD), and has been heretofore configured as a so-called exclusive-machine type (also called as a fixed type, etc.) configured integrally with a support base. Recently, there has been developed and come into practical use a portable radiographic image capturing apparatus which houses the radiation detecting elements and the like in a housing so that those elements and the like become portable.
In such a radiographic image capturing apparatus, as illustrated in FIG. 3 to be mentioned later for example, generally a plurality of radiation detecting elements 7 are arranged in the state of a two-dimensional matrix on a detecting section P. When the radiographic image capturing apparatus is irradiated with radiation through a not-illustrated patient as an object at the time of imaging, the radiation detecting elements 7 generate the electric charges. To each of the radiation detecting elements 7, a switch element composed of a Thin Film Transistor (hereinafter referred to as a TFT) 8 and the like is connected. In a readout processing of image data D after the imaging, when the TFT 8 is turned on so that the electric charges accumulated in the radiation detecting elements 7 are discharged into signal lines 6, the electric charges flow into readout circuits 17 through the signal lines 6, and are read out as electric charge data D in the readout circuits 17. The readout processing of the image data D will be described later.
Meanwhile, in the case that imaging using the radiographic image capturing apparatus is not performed at least for a while, the power applied to respective functional sections such as the readout circuits 17 of the radiographic image capturing apparatus is wasted. Especially in the above-described portable radiographic image capturing apparatus including a battery, if the power is thus wasted, the battery would be consumed earlier, the number of time of the imaging on one battery charge would be reduced, and imaging efficiency would be reduced. Those have been problems.
For this reason, there have been not a little radiographic image capturing apparatuses configured to have an imaging mode including at least: a wake up mode in which the power is applied to the respective functional sections so that the imaging can be performed; and a sleep mode in which the power is applied to required minimum functional sections and the imaging cannot be performed, wherein the imaging mode can be switched between these modes (e.g. see Japanese Patent Application Laid-open No. 2010-268171). The above-described readout circuits 17 consume relatively large power at the time of the readout operation of the image data D and the like. For this reason, in the sleep mode, generally the radiographic image capturing apparatus does not perform at least the readout operations in the readout circuits 17.
In the meantime, according to the research by the inventor, it has been found that when the imaging is performed after the power mode of the radiographic image capturing apparatus 1 is switched to the sleep mode and then switched to the imagable mode again, sometimes image unevenness and/or stripe pattern appear, though only slightly, in a radiographic image I generated based on the image data D which has been read out after the imaging (see FIG. 7). In FIG. 7, the image unevenness and the stripe pattern appearing in the radiographic image I are emphatically illustrated.
As described later, generally a predetermined number (e.g. 128, 256, etc.) of the readout circuits 17 are provided in one readout IC 16 (see FIG. 3 to be mentioned later), and a necessary number of readout ICs 16 are arranged in parallel depending on the number of signal lines 6 or the like. According to the research of the inventor, as illustrated in FIG. 7, the image unevenness in the radiographic image I appears in each of regions R1, R2, R3, R4, . . . corresponding to the readout ICs 16, respectively, and the strip pattern appears in positions corresponding to the readout circuits 17.
Concretely, the signal lines 6 are connected to the readout circuits 17, respectively, and the predetermined number of the signal lines 6 are connected to each of the readout ICs 16, as described above. When paying attention to each of regions R1, R2, R3, R4, . . . in the radiographic image I corresponding to the respective readout ICs 16, a certain offset is superimposed on the image data D of pixels within each one of the regions R. The certain offset is different according to each of the readout ICs 16. The superimposed offset appears as the image unevenness in each of regions R1, R2, R3, R4, . . . . Additionally, it has also been found that offsets are superimposed on the image data D of pixels correspondingly to the signal lines 6 connected to the readout circuits 17, respectively, which offsets appear as the stripe pattern in the radiographic image I.
As a result of accumulation of research by the inventor, the cause of superimposition of the offset which causes image unevenness and/or stripe pattern on the image data D has been found, and also the configuration to prevent such a phenomenon from occurring has been found.